Pipeline Condition Detecting Method and Apparatus

ABSTRACT

The current invention relates to an apparatus for detecting at least one characteristic of a pipeline. The apparatus includes means for generating a magnetic flux along a portion of a pipeline wall, means for detecting the magnetic field, and at least one proximity sensor. The apparatus further includes means for generating an indication of whether defects are located in the internal or external wall of the pipeline.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of pending U.S. applicationSer. No. 12/743,133 filed Aug. 5, 2010, which is the National Phase ofPCT Application No. PCT/GB2008/003847 (Publication No. WO2009/063218)filed 17 Nov. 2008 which claims priority to British Patent ApplicationNo. 0722534.5 filed 16 Nov. 2007.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE

Not Applicable

BACKGROUND OF THE INVENTION

The invention which is the subject of this application is directedtowards a method and apparatus which allows the condition of a pipeline,or predetermined length of the same, to be predicted and assessmentsthen made as to any remedial work which may be required in a reliableand efficient manner.

The condition of pipelines which are used to carry fluids willdeteriorate over time. The rate of deterioration may vary over thelength of the pipeline and with respect to other conditions which mayprevail on the pipeline such as the type of material carried along thepipeline and environmental conditions surrounding the pipeline.

There are many forms of apparatus which may be used to attempt todetermine the condition of pipelines and one such form of apparatus isdisclosed in the applicant's patent application EP 1262771. In thisdocument there is provided apparatus and a method of identifying thepresence of a defect in the pipeline and also determining whether thedefect is present on the interior or exterior surfaces of the wall ofthe pipeline. The contents of that document are incorporated herein byreference thereto.

In order to assess the condition of a pipeline it is generally requiredto be able to determine the known pipe wall deterioration rates for theparticular pipeline in question, the loading regimes applied to thepipeline, the drivers which may cause corrosion of the pipeline andwhether or not any, and what type, of corrosion protection has beenused.

BRIEF SUMMARY OF THE INVENTION

The aim of the present invention is to provide a method which allows thecondition of the pipeline to be determined accurately along apredetermined length of the same, without having to inspect the whole ofsaid predetermined length. As one will appreciate, it is necessary forthe method of the invention to be reliable in order to ensure that themeasurements made, and the predictions made on the basis of thosemeasurements, are accurate and reliable.

In a first aspect of the invention there is provided a method fordetecting the condition of a length of pipeline, said method comprisingthe steps of, identifying at least one portion of the length of pipelinewhich is to be tested, measuring for that said portion at least thecondition of the pipe wall, wherein the condition of the pipe wall ismeasured along the length of the portion and around at least part of thecircumference of said portion of the pipeline.

Typically, when access of the apparatus is permitted and/or possible,the entire circumference of the portion of pipeline will be inspected.

In one embodiment the method includes the further step of measuring thecondition of the pipeline protective coating if one is provided. In oneembodiment the method includes the further step of determining thecharacteristics of the soil in the vicinity of the pipeline.

Typically the method includes the step of predicting the condition ofthe pipeline length based on the measurements taken with respect to thesaid portion or portions.

In one embodiment, based on the predictions, any required remedialactions can be taken at that time and/or can be scheduled for futureperformance.

In one embodiment, the prediction made can be determined on the basis ofpreviously known data and measured data.

In one embodiment the portion of the pipeline which is selected is thatwhich is regarded as being located in a critical part of the pipelineand/or located in that part of the pipeline which is regarded as beingmost susceptible to deterioration or most heavily loaded. Alternativelythe portion or portions can be selected randomly along the length of thepipeline.

In one embodiment the number of defects in a given portion of thepipeline are determined and assessed as to whether there is a sufficientnumber to allow the analysis to be performed. If there is aninsufficient number then the length of the portion which is assessedwill be increased or alternatively the condition of the pipeline isdetermined to be acceptable for a period of time in the future.

In one embodiment the soil condition is determined by measuring the pH,resistivity, redox potential, ground type, moisture content and/orheterogeneity of the same.

In addition or alternatively the soil condition is determined by usingapparatus comprising a plurality of electrodes which are inserted intothe soil, one of said electrodes typically being formed of copper, onebeing formed of a similar material to that used to form the pipeline anda standard electrode and are recorded and processed to provide a linearpolarisation resistance (LPR) reading factorised with other measuredsoil parameters including redox.

In one embodiment the electrodes are inserted into the soil to a depthof at least 15 cm and are all located within the length of the portionof the pipeline.

In one embodiment, when there, is a need to test the condition of thecoating of the pipeline, the coating along and around the portion of thepipeline is exposed and the same is visually inspected with reference toa recording grid, each cell of the grid representing an identifiedlocation of the coating of said pipeline portion. An indication is thenprovided for each cell representing whether the coating in that cell isbetter than, worse than or similar to a datum which may, in one example,be the expected condition of the coating of the particular age on theparticular pipeline type.

In addition, or alternatively, apparatus may be used to allow thecondition of the coating to be analysed from above ground as an aid toselecting the optimum locations for pipeline inspection. In this casePipe Current Mapper (PCM) apparatus may be used to pass a signal alongthe pipeline portion. If the signal is detected as having increased overa specific section along the pipe then this is an indication of thefailure of the coating or the coating being poorer condition on thatsection as the coating is not masking the signal to the same extent asthe reminder of the coating on the portion.

In one embodiment, in order to measure the condition of the pipelinewall, detection apparatus is moved along the portion and around thecircumference of the said portion of pipeline so as to provide themeasured readings as required. The measurement around the circumferenceof the pipeline is required as it is found that corrosion patterns canvary around the pipeline.

Typically the apparatus provides location data which indicates theparticular location of the apparatus and hence the location of thereadings which are being obtained at that time with respect to thepipeline portion.

Typically when the pipeline is steel or iron the apparatus includes ameans for generating a magnetic flux, into the pipeline wall, means formonitoring the flux level and proximity sensing means. In one embodimentthe apparatus includes means for providing azimuth data so as todetermine the position of the apparatus around the pipelinecircumference as well as along the length of the portion of the same.

Alternatively, if the pipeline is of a material with which ultrasonic ormagnetic sensors cannot be used (such as concrete) a ground penetratingradar (GPR) device can be used to be placed onto the pipeline andprovide data readings representative of the condition of the pipelinewall and in particular the degree and depth of pitting of the same.Typically a means for measuring the azimuth position will also beincorporated.

Typically to allow the prediction of leakage to be performed thedetection of the condition of the pipeline portion is made with respectto assessing the level of the pitting of the pipeline wall. Once againthe pipeline portion is represented as a grid of cells and a measurementof the degree of pitting is performed using the apparatus for each celllocation and a value is provided. Typically, for each cell, the depth ofthe deepest pit is also measured and recorded.

In one embodiment this process is performed with respect to the deepestpit in each grid square which is, identified as depending from the outerwall of the pipeline inwardly and from the inner wall of the pipelineoutwardly.

In one embodiment all other defects which are detected are ignored.

Typically this data is then processed to provide a predicted pattern offailure of the pipeline on an ongoing basis.

Typically the potential of structural failure of the pipeline portion isassessed with respect to individual defects and larger areas of pipewall corrosion. In one embodiment this assessment is performed withreference to available data and measured data such as any or anycombination of road and ground loading models, fracture potential of thepipeline, the soil analysis, temperature variations, measured currentpipe wall thickness and/or the pitting measurements, and the conditionof the pipeline coating if provided.

In one embodiment the length of the portion of the pipeline which isbeing measured can be selected to suit specific requirements. However itis found that a length of 1 metre can be sufficient for any givenportion. In one embodiment a series of portions may be selected atspaced intervals long the length of the pipeline and each of theseportions is measured in accordance with the method of the invention. Inone embodiment the particular length of the portion of the pipeline andthe measuring width of the apparatus are matched such that the apparatusas a whole does not need to be moved along the pipeline portion whenmeasuring the portion and in this case the apparatus need only be movedaround the pipeline portion circumference.

Typically when preparing the prediction of the pipeline condition basedon the measured portions and/or determining maintenance requirementsbased on the predictions, suitable algorithms may be used into which themeasured and predetermined data can be input as appropriate.

In one embodiment a database of data is prepared and generated on anongoing basis. In one embodiment the database includes data frompublicly available reference materials and/or data which is obtainedfrom previously performed pipeline measurements. In one embodiment thedata from previously performed measurements can be cross referenced withcertain parameters such as soil type, geographical location, and/ordepth of pipeline such that when subsequent reference is made to thedata, the same can be assessed for suitability with respect to thesecharacteristics in relation to the pipeline which is being assessed atthat time.

In one embodiment the method includes the step of updating the databasewith measurement data from pipeline portions on an ongoing basis.

In accordance with the invention, by performing the measurement steps asherein indicated on portions of the pipeline, this measured data can beused in conjunction with known reference data to provide an accurateprediction of the condition of the remainder of the said length ofpipeline. This prediction can then be used to determine whether thepipeline is in an acceptable condition at that time of measurement andalso, if required, to provide an ongoing prediction of the condition ofthe pipeline over a time interval going forward. On the basis of thesepredictions remedial works can be scheduled for the pipeline therebyminimising the risk of potentially damaging and unexpected pipelinefailure.

Typically the number of portions which are selected along the length ofthe pipeline are such as to ensure that at least minimum number ofdefects are identified so as to allow the subsequent assessment which isperformed to be statistically valid. In one embodiment the number ofdefects required to be identified are 12 or more with respect to themonitoring of the pitting of the pipeline wall.

Typically each portion of the pipeline is represented by a grid and foreach cell of the grid an assessment is made of the condition of thepipeline and a value is allocated. However it should be noted that forcertain measurements such as, for example, measurement of the pitting ofthe pipeline wall, only one pit defect, typically the deepest, in eachcell is counted as a defect, this is regardless of how many other pitsmay be located in that cell. This therefore means that when the minimumnumber of defects is being assessed only one defect per cell can betaken into account.

In one embodiment the size of the grid can be selected to represent aparticular portion length and circumference of the pipeline in eachinstance.

Typically the prediction of failure of the pipeline at some stage in thefuture is undertaken using statistical analysis.

In a further aspect of the invention there is provided apparatus for thedetection of at least one characteristic of a pipeline, said apparatuscomprising a body including means for generating a magnetic flux along aportion of the pipeline wall, a means for detecting the magnetic fieldcreated and at least one proximity sensor wherein said apparatusincludes means for generating an indication of whether any defectslocated arise on the internal or external wall of the pipeline.

In one embodiment azimuth data is generated to indicate the location ofthe apparatus with respect to the circumference.

Typically the apparatus is used to detect the presence of pittingdepending inwardly from the external and/or internal walls of thepipeline. Typically the pipeline to be tested is formed of a metal.

In one embodiment the measuring apparatus is adapted to minimise thenoise which may affect the monitoring. In one embodiment the electroniccircuitry is provided on a single board in the body and/or the tyres onwhich the apparatus body is supported and movable are formed of lowvibration material such as rubber or another similar material and/ormagnetic detection means are used so as to reduce vibration.

In one embodiment the electronic circuitry is carried as a separate partto the monitoring apparatus body, thereby reducing noise and/or thephysical size of the apparatus body which is required to be positionedat the pipeline thereby improving the accessibility of the apparatus.

In one embodiment data received from the apparatus on the pipeline ispassed for analysis and plotting in real time.

In one embodiment the monitoring apparatus body placed at or adjacent tothe pipeline is modular and can be increased or decreased in lengthand/or width so as to allow the same to be adapted for the specificmonitoring to be performed.

In one embodiment an air gap is provided between the body, which carriesthe electromagnetic coils for generating the magnetic flux, and thepipeline being monitored. In one embodiment the air gap is crossed by aseries of spaced conductive wires mounted in the body, said wiressufficiently flexible to flex when the apparatus is moved but alsoretain contact between the pipeline and apparatus body to allow themagnetic flux generated from the body into the pipeline to then passalong the wires which form the return path between the pipe and thebody.

The provision of these wires typically allows a reduction in the numberof coils which are required to be provided in the apparatus body togenerate sufficient magnetic flux.

In one embodiment the wires are provided as a series of bristles, saidbristles provided in spaced groups across the underside of theapparatus.

In one embodiment the body can be formed as a modular unit of, forexample, first and second modules, with a first module being used alonefor certain pipe monitoring requirements and, in other embodiments asecond module can be placed on the first module to form the body.Typically each of the modules includes electromagnetic coils and so,where stronger magnetic flux is required to be generated, such as forlarger pipelines, the two modules are used together in a stackedconfiguration.

In one embodiment the sensors used in the apparatus are bidirectionalsensors, or alternatively tri-directional sensors.

Typically the apparatus includes one or more guide means which allow theguided movement of the body along the portion of the pipeline which isto be monitored. Typically, in addition further guide means are providedto allow the body to be moved circumferentially around the said pipelineportion.

In a further aspect of the invention there is provided apparatus fordetecting the condition of a pipeline wall, said apparatus including aGPR device which is movable along the surface of the wall, said devicetransmitting signals which can be processed to indicate the depth of thewall surface with respect to a datum at each location.

In a yet further aspect of the invention there is provided a method oftesting the condition of a pipeline, said method comprising the steps ofdetermining a portion of the pipeline to be used as a sample to betested, performing at least one test to determine a condition of thesame wherein, if the number of defects detected is below a predeterminedlevel, the condition of the pipeline is deemed to be acceptable and, ifabove the predetermined level, further testing of the pipeline isperformed.

In one embodiment the defect data used includes a prediction of thedepth of the defects in the pipeline wall.

Typically, if the condition of the pipeline is deemed to be acceptable,no further testing is performed.

In one embodiment the further testing is followed by statisticalanalysis of the test results.

In one embodiment the method includes the steps of assessing thecondition of the soil and the corrosovity of the material from which thepipeline is formed and/or the condition of any coating of the pipeline.

Typically the analysis provides information relating to the currentcondition of the pipeline and also the future condition of the pipelineover a number of years.

In one embodiment structural defects of the pipeline can be assessed andselectively used as part of the pipeline condition analysis.

In one embodiment the average wall thickness is assessed.

In one embodiment the portion to be used as the test sample is selectedrandomly or alternatively, is selected as a portion which can berelatively easily accessed, such as the closest accessible point to arandomly selected location.

Typically all defects in the selected portion are recorded and thosedeemed not to be relevant are subsequently discarded.

In one embodiment the condition assessment of the pipeline is given fora predetermined length or the entire length of the pipeline.

In one embodiment the analysis includes a comparison of thepredetermined loading values along the length of the pipeline and thepredicted defects and the probability of the different conditionscoinciding such as, for example, high loading occurring at the samelocation as a high level of defects which would further increase therisk of failure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Specific embodiments of the invention are now described with referenceto the accompanying drawings wherein

FIG. 1 illustrates a length of pipeline which can be assessed inaccordance with the invention;

FIG. 2 illustrates one possible form of apparatus for assessing soilconditions in the vicinity of the portion of pipeline being measured;

FIGS. 3 a and b illustrates the method followed in assessing thecondition of the coating of said pipeline portion;

FIG. 4 illustrates the method followed in assessing the condition of thepipeline wall;

FIGS. 5 a-c illustrate embodiments of the apparatus which may be used toperform the measurements required for FIG. 4; and

FIG. 6 illustrates a grid of results obtained using the apparatus ofFIGS. 5 a-c.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to FIG. 1 there is illustrated a length of pipeline 2which is to be assessed and for which a prediction of its condition isto be determined.

The pipeline can be of a number of kilometres in length and inaccordance with the invention at least one, and in the example showntwo, portions 4 of the pipeline are selected to be measured. Theportions which are selected may be selected to be at a location which isidentified as being most prone to corrosion and therefore can be said tobe most likely to be in the worst condition along the length of thepipeline or may be at locations where the maximum of the combinedloading regimes are being applied or may be randomly selected to berepresentative of the deterioration of the length of pipeline.

With the portion to be measured having been determined, then inaccordance with the invention the condition of the soil 6 in thevicinity of the pipeline portion 4 is required to be assessed. In oneembodiment this can be achieved by using the apparatus as shown in FIG.2 in which electrodes 7,8,10 are placed into the soil above the portionof the pipe. Typically, one of the electrodes is of copper, one of theelectrodes is of the same material as the pipe walls and the otherelectrode is of a standard selected material. The electrodes areconnected to a processing device 12 and the data received is used togenerate a graphical representation 14 as shown in FIG. 2 which isrepresentative of a Redox Factorised linear polarisation resistance(LPR). This can be repeated for each of the measured portions of thepipeline to determine whether the soil type is the same at each portionlocation or not.

Other soil condition factors such as pH, ground type, moisture contentand heterogeneity may also be measured and taken into account to give anindication of the soil type.

Most pipelines include a coating material on the external surface of thesame in order to try and protect the pipeline wall from corrosion andthe condition of this coating (if provided) is assessed in accordancewith the invention.

In accordance with the embodiment shown in FIG. 3 this is achieved byexposing the coating around the periphery of and along the length of theportions 4 of the pipeline and performing a visual check. The pipelineportion is represented by a grid 16 and FIG. 3 a illustrates how thisgrid effectively is mapped around the periphery of the coating of thepipeline portion 4. Each cell 17 of the grid 16 is provided with acoordinate 18 relating to the position round the circumference of thepipeline and a coordinate 20 relating to the position along the lengthof the pipeline. For example the cell 17 shown by the reference arrowshas the co-ordinates B800-900 on the grid 16. The size of the grid canbe selected to suit the pipeline in question as can the size of area ofthe pipeline represented by each of the cells. In one embodiment thewidth of the portion is equivalent to the length of pipeline which canbe measured by monitoring apparatus without having to move the apparatusas a whole along the pipeline portion.

For each cell 17 a value is allocated to the percentage of the coatingfailure at that cell location. This value may in one embodiment be withrespect to the range of no coating to full coating or alternatively maybe with respect to an “average” coating value. The values are thenassessed and the areas with the coating condition below a certain levelcan be identified in this case by darker shading of the cells.

In addition, or alternatively to the above, a PCM signal may betransmitted along the pipeline portion and detection means are mountedexternally of the pipeline to identify the same. Typically the provisionof the coating will act to mask or damp the signal to a reduced strengthwhen detected externally of the pipeline. However if the coating isremoved or thinner at any location on the portion the signal will bedetected as having a greater strength thereby indicating the poorcondition of the coating at that location. Thus in accordance with thisembodiment the grid cells can again be filled with a reading indicativeof the condition of the coating at that cell but the reading can beobtained from a position above ground via the signal detection meansthereby avoiding the need for the pipeline portion to be available for avisual inspection.

In accordance with the invention the condition of the pipeline wall isassessed with reference to the pitting of the wall. The assessment maybe made with regard to the occurrence of pitting regardless of whetherthe same depend from the external or internal surface of the pipelinewall, or, alternatively the location of the pitting with respect to theinternal or external surfaces can also be identified. In either case theassessment is performed along the length of the portion and also aroundthe circumference of the portion of the pipeline portion. The dataindicative of the pitting is logged and mapped onto a grid 20 with aseries of cells 21 with coordinates so that the location of the pittingis mapped to a specific location on the pipeline portion. An example ofthe grid 22 is provided in FIG. 4 with each of the cells 21 having acorrosion value allocated thereto. Once more the grid is mapped to thepipeline portion 4 in a similar manner and with the same co-ordinates asindicated in FIG. 3 a.

It is also possible, in one embodiment, for the loading characteristicsof the length of pipeline to be determined and this information to beused in conjunction with results obtained for the inspection fordefects. For example, if, on the basis of this analysis it is determinedthat a location of high loading somewhere along the pipeline willcoincide with a predicted location of high defects then this will behighlighted and may result in remedial work being required to beperformed immediately or at least earlier in a schedule of repairs thanwould otherwise have been envisaged. The same applies to a location onthe pipeline wherein the loading is relatively low in which casepredicted defects at that location are given less significance in theoverall analysis and prediction of the pipeline condition.

In whichever embodiment it is desired that the circumference of thepipeline portion needs to be inspected. The number of portions which areinspected along the length of the pipeline is typically influenced bythe need to identify and measure at least a minimum number ofstatistically valid number of pitting occurrences. For each cell wherethere is pitting only one pitting occurrence in that cell counts as adefect.

When the pipeline material is metallic, the monitoring apparatus usedcomprises means for emitting a magnetic flux or field. The magnetic fluxis induced by the conductor apparatus 24 which has a body 40 whichcauses generation and movement of the magnetic flux from the body intothe pipeline wall 4 and to return to the body 40. When the interior andexterior surfaces of the pipeline are smooth, and generally fault freethe return magnetic flux level is similar to that sent from the body tothe pipeline but the location of a defect such as pitting, causesleakage of magnetic flux through the pipeline wall and the change inmagnetic flux is monitored by monitoring means which can be provided onthe body and connected to processing means which can also be provided onthe body or connected thereto and carried separately so as to minimisethe size of the body and minimise vibration.

The apparatus body is fitted with wheels and, if required, a suspensionsystem, that serve to facilitate movement of the apparatus along thepipe section 25 being inspected, and to maintain an air gap 44 betweenthe pipeline wall and the underside of the body. This system allowsadjustments to be made in order to accommodate variations in pipegeometry. The apparatus body 40 is typically located on guide means inthe form of a frame and one example of the same is provided in FIG. 5 a.As shown in FIG. 5 a the detecting head 24 is capable of moving in thedirection of arrow 25 along the length of the frame 26 and the frameitself is capable of being moved around the circumference of thepipeline wall 4, possibly on further guide means (not shown) so that itwill be appreciated that the entire portion of the pipeline can be interms of length of the same and circumference of the same assumingaccess is possible.

Proximity sensors are also provided in the body 40 which are sensitiveto the presence of the pipe material beneath it. When passing along apipe showing no or insignificant corrosion a constant output signal interms of volts would be expected to be received from the proximitysensors. However, if a change in condition is detected on or near theexternal surface of the pipeline the proximity sensor reading willchange.

The detector array is moved by pulling it by hand, along the guidemeans, thus scanning the pipe section below it. The guide means and bodythereon can then be moved in stages circumferentially around the pipe toallow adjacent pipe lengths to be inspected. This process continuesuntil preferably the entire pipe circumference has been inspected.

The body typically consists of two electromagnets 31, 35 which arelocated on the body to provide a return magnetic flux path between themand through the pipeline wall 4. When this assembly is placed on thetrack above the pipe being inspected the pipe structure provides thefinal element in the magnetic flux flow path.

In one embodiment the body further includes magnetic flux leakagemonitors 32 in the form of Hall effect sensors fixed into the body alongwith proximity sensors. The body is also fitted with a means ofrecording its position relative to the guide means and hence in relationto the pipe section 4 being scanned.

When the body 40 is passed along the portion, if the proximity sensorsshow no or insignificant corrosion a constant output signal is generatedto be received from the proximity sensors. However the proximity sensorscan detect the interface between, for example, a graphite layer and theoriginal pipe material of a cast iron pipe and register the change bythe change in received voltage as the body passes over the corroded areaif that area is at or near the external surface of the pipeline.However, the proximity sensors do not react in this way when moving overan area of the pipe with corrosion at or near the internal wall of thepipeline as the proximity sensor is set so as not to detect through thedepth of the pipe wall. In this way the detector array can detect anddistinguish between external and internal corrosion, as firstly themagnetic flux detection detects corrosion at any position in thepipeline wall and the proximity sensor only reacts if the corrosion isat or near the external surface of the pipeline.

The strength of the detected magnetic flux or field is used to determinethe presence of pitting in the pipeline wall and the one or moreproximity sensors allow the determination of whether the pitting ispresent in the internal or external surface of the pipeline wall.

FIG. 5 c illustrates a further embodiment of apparatus which can beused. Where appropriate the same reference numerals are used for thesame components. In this case the body 40 of the apparatus is providedto run along the length of track to be tested along guide means 26, withhandles (not shown) typically being provided to allow the body to bemanually moved. Wheels 46 are provided on the body to engage and movealong the guide means, with the wheels being formed of a material tominimise vibration as the same move along the track. The body 40 in thiscase is shown formed of one modular unit, but, if required to generate astronger magnetic flux to inspect or monitor the pipeline wall, forexample a pipeline wall 4 of greater depth, a second modular unit 40′,shown in broken lines, can be attached to the first modular unit andelectrically connected, typically in a stacked configuration. The body40 also includes hall effect sensors 32 and proximity sensors mountedtherein and it should be appreciated that the particular configurationof the same will be selected to suit specific requirements.

An air gap 44 is provided between the underside of the body and theexternal wall of the pipeline. The apparatus can be used with the airgap or, as shown in this embodiment, the air gap can be bridged bygroups of wires or bristles 50 which are mounted on the underside of thebody and the free ends of the same contact with the pipeline wall asshown. It is found that the spaced array of groups of bristles or wiresallows the number of coils of the electromagnets to be reduced andgenerally provides a more reliable monitoring performance as themagnetic flux can be carried along the conducting wires particularlyfrom the pipeline to the body to allow the return magnetic flux to bemonitored by sensors 32.

Typically the bristles or wires are sufficiently flexible to allow thesame to flex when the body is moved while at the same time beingsufficiently rigid so as to maintain the contact between the pipelineand the body.

In addition to detecting the presence of pitting, the depth of at leastthe deepest pit in each cell is determined and mapped onto a grid asshown in FIG. 6. Thus, the frequency and spread of the pitting isidentified and also those areas where the pitting is deepest, and hencethe pipe wall thinnest, are identified.

In certain cases the material from which the pipeline wall is formedprevents the uses of the magnetic field detection means. In this casealternative apparatus in the form of a GPR device can be used. The GPRdevice can be used in a similar manner to that described above with thedetection head being moved along and around the portion so as to allowindicative readings to be obtained.

With this measurement data available, the same can then be graphicallyrepresented and processed such that, for example, data relating to thecurrent deepest pitting and number of critical defects can be used toprovide predicted values for the future defects and future criticaldefect patterns.

These predictions can be made by using statistical analysis, typicallyutilising suitable algorithms into which the measured data can be inputas appropriate. In addition to the measured data other reference dataand/or data from previous pipeline measurements which are applicable tothe current pipeline being measured may be selectively obtained from areference database and used as required in the algorithms in order toprovide an accurate and reliable prediction for the whole of thepipeline length to which the assessment is being applied rather thanjust the portions which have been measured.

Other predictions which may be provided include predicted internal andexternal pipeline wall defect patterns over the defined length ofpipeline as the likely ongoing corrosion rate can be calculated withreference to the measured data and known reference data. The predictedyear of structural failure may also be provided with reference to themeasured wall thickness and calculated critical wall defects and otherreference data such as the maximum loading regime on the pipeline.Predictions of the effect of reducing or increasing the combined loadingregimes on the year of failure can also be made.

It will therefore be appreciated that the current invention providesapparatus and a method which allows the scanning of the condition of atleast one portion of pipeline to be performed in an efficient andreliable manner, and as a result the measured data can be used toprovide an accurate indication of the condition of a length of thepipeline in which the said at least one portion is located.

1. Apparatus for the detection of at least one characteristic of apipeline, said apparatus comprising a body including means forgenerating a magnetic flux along a portion of the pipeline wall, a meansfor detecting the magnetic field created and at least one proximitysensor wherein said apparatus includes means for generating anindication of whether any defects located arise on the internal wall orexternal wall of the pipeline.
 2. Apparatus according to claim 1 whereinthe apparatus includes means for generating azimuth data to indicate thelocation of the apparatus with respect to the circumference of thepipeline.
 3. Apparatus according to claim 1 wherein the apparatus isused to detect the presence of pitting depending inwardly from theexternal wall or internal wall of the pipeline.
 4. Apparatus accordingto claim 1 wherein electronic circuitry is provided on a single printedcircuit board in the body.
 5. Apparatus according to claim 4 wherein theelectronic circuitry is carried as a separate part to the monitoringapparatus body.
 6. Apparatus according to claim 1 wherein the body ismodular and can be increased or decreased in length and/or width so asto allow the same to be adapted for the specific monitoring task to beperformed.
 7. Apparatus according to claim 1 wherein the body can beselectively formed from a series of modules, each of said modulesincluding at least one means to generate a magnetic flux and theselection of the number of modules for a monitoring task is made withrespect to the strength of magnetic flux required.
 8. Apparatusaccording to claim 1 wherein an air gap is provided between the body andthe pipeline being monitored.
 9. Apparatus according to claim 8 whereinthe air gap is crossed by a series of spaced conductive wires mounted onthe body.
 10. Apparatus according to claim 9 wherein the said wiresretain contact between the pipeline and body to allow the magnetic fluxgenerated from the body into the pipeline to pass along the wires. 11.Apparatus according to claim 10 wherein the wires are provided as aseries of bristles, said bristles provided in spaced groups across theunderside of the body.
 12. Apparatus according to claim 1 wherein thesensors used in the apparatus are bidirectional or tri directionalsensors.
 13. Apparatus according to claim 1 wherein the apparatusincludes one or more guide means which allow the guided movement of thebody along the portion of the pipeline which is to be monitored. 14.Apparatus according to claim 13 wherein guide means are provided toallow the body to be moved circumferentially around the pipeline portionwhich is to be monitored.
 15. Apparatus according to claim 1 wherein theapparatus further includes a grid comprising a plurality of cells, eachcell allocated to a particular location area on said portion ofpipeline, and providing for each cell data obtained from the sensors ofthe apparatus for the particular pipeline location area to which thecell is allocated.
 16. Apparatus according to claim 1 wherein saidapparatus includes a ground penetrating radar device which is movablealong the surface of the wall, said device transmitting signals whichcan be processed to indicate the depth of the wall surface with respectto a predetermined datum thickness value.
 17. Apparatus according toclaim 1 wherein the apparatus includes wheels which contact guide meansmounted on the pipeline or the pipeline to facilitate movement of theapparatus with respect to the pipeline.